British artist Kit Williams published Masquerade, a children's book which combined fantasy storytelling with a real-world treasure hunt. The 1979 book tells a whimsical story about the moon sending a golden hare sculpture as a gift to the sun, with a rabbit named Jack Hare acting as the messenger. However, Jack loses the gift on his journey, and readers are challenged to find it themselves, in real life—prompting a national treasure hunt across Britain. The treasure was real: an 18-karat gold hare adorned with jewels, hidden somewhere in the countryside.

Attribution:
Picture 16294003526 - The Queen Catherine of Aragon Monument at Ampthill
by Jayembee69
CC BY-NC-SA 2.0.
https://creativecommons.org/licenses/by-nc-sa/2.0/